What substitution should be used to rewrite 6 times open paren x plus 5 close paren squared plus 5 times open paren x plus 5 close paren minus 4 is equal to 0 as a quadratic equation?

The expression that appears repeatedly is x + 5: it is squared in the first term and appears by itself in the second term. Substitute u = x + 5, so the equation becomes 6u² + 5u − 4 = 0, a quadratic equation in u. Therefore, the correct choice is “u is equal to (x + 5).”

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